This invention relates to web tensioning apparatus, and more particularly to web tensioning apparatus for maintaining the tension in a web traveling through a hostile fluid bath.
In the processing of a continuous web formed of material, such as flexible printed circuit board material, it is often necessary to pass the web through a hostile fluid bath such as an etching or plating bath. Conventionally, the web is passed alternately between two series of spaced, parallel rollers that are mounted for rotation upon fixed bearings, one series being located in the bath itself and the other series between located above the bath. The series above the bath are machined to a high degree of identity and driven from a common mechanical power source so as to have substantially identical surface velocities. The series within the bath are idled. Associated with this arrangement, however, are a number of significant problems. First, uncontrollable tension increases and decreases occur in the web, because of the cumulative effect of minute differences in the surface speeds of the rollers. As a result, the web may be damaged or broken. If the web breaks, all processing equipment must be stopped until the web is guided back through the equipment. Second, accurate guidance of the lateral position of the web is made difficult due to the mentioned tension increases and decreases. Gross errors in the lateral position of the web result from the tension increases and decreases, and as a consequence, further damage may be done to the web. Third, because the lower rollers and their bearings operate within the hostile environment of the bath, extraordinary costs must be incurred for bearing repairs and replacements, and for the resultant reduction in operating efficiency.